In a wafer (hereinafter, referred to as “pattern wafer”) having a predetermined pattern for manufacturing electronic devices, a silicon oxide film formed by CMP (Chemical Mechanical Polishing) or the like may exist on a surface of a polysilicon layer. The silicon oxide film serves as a mask in etching the polysilicon layer and inhibits etching of the polysilicon layer. Therefore, an etching process for removing the silicon oxide film is performed on the pattern wafer before the etching of the polysilicon layer. The etching process for removing the silicon oxide film is referred to as “break-through process”.
The pattern wafer that has been subjected to the break-through process is subjected to an etching process (hereinafter, referred to as “main etching process”) for removing the polysilicon layer. However, the polysilicon layer may not be completely removed by the main etching process. In that case, a silicon residue remains on the pattern wafer.
In order to remove the residue, an overetching process in which the main etching process is continued is performed even after the polysilicon layer is substantially completely removed. In addition, there is suggested a technique for introducing a plasma cleaning gas for removing a residue after a main etching process (see, e.g., Japanese Patent Application Publication No. H7-508313) or a technique for changing a residue to a water-soluble residue and removing the water-soluble residue by performing gas plasma treatment on a pattern wafer (see, e.g., Japanese Patent Application Publication No. H11-260785).
However, the electronic devices may be damaged in the case of introducing the plasma cleaning gas after the overetching process or the main etching process or in the case of performing the gas plasma treatment.